The following reference are believed to represent the state of the art:
An article entitle “2D code” and an article entitled “Data Matrix” in the Wikipedia website; and
An article entitled “The iTV Doctor Is In!: Mobio CEO, Clovis Najm, on Using QR Codes to Enable Interactive TV via Companion Devices” at itvt.com/itv_doctor/7544/itv-doctor-mobio-ceo-clovis-najm-using-qr-codes-enable-interactive-tv-companion-devi.